The unauthorized removal of articles from a surveillance area may be deterred by attaching tags including inductor/capacitor resonant circuits to articles within the surveillance area and generating an electromagnetic field of predetermined frequency in a controlled area to detect the passage of tagged articles therethrough. The tag circuit, which resonates at the frequency of the electromagnetic field, may be detected by the receiving component of an EAS system to indicate the unauthorized removal of the tagged article from the surveillance area.
To prevent the tag from activating the security system when the tagged article is to be legitimately removed from the surveillance area, the tag must either be removed or deactivated. Removal of tags is both labor and time intensive and therefore is generally considered to be too inefficient to be employed. Deactivatible EAS tags are disclosed in U.S. Pat. No. 4,498,076, which is hereby incorporated by reference. It is preferred that the tag be deactivated by exposure to an electromagnetic field of corresponding frequency and sufficient power to effectively overload and short-circuit the capacitor portion of the tag so that the tag no longer resonates at the frequency of the EAS system, if at all.
To reduce the possibility of accidentally deactivating a tag circuit, it is preferred that the energy transmitted for deactivation be confined to a relatively small area. To meet federal emission regulations and emission regulations of other countries, the preferred deactivation antenna employed for radiating deactivation energy must effectively cancel far field radiation.
For aesthetic and practical reasons, it is also desirable to have an unobtrusive deactivation antenna. For example, retail establishments generally prefer unobtrusive antennas to avoid offending customers. It would be particularly advantageous to have available a substantially planar deactivating antenna small enough to be incorporated into a standard checkout counter, yet strong enough to withstand rigorous daily use.
The effectiveness of many prior art deactivation antennas is often contingent upon the orientation of the tag with respect to the antenna. For example, some prior art deactivation antennas require that the tag be aligned face down and in the center of the antenna in order to achieve effective deactivation. It would be advantageous to have a deactivation antenna wherein the orientation of the tag does not hinder the deactivation process, i.e., the tag can be deactivated without having to be placed in a particular orientation. The present invention overcomes the shortcomings discussed above, as well as many other shortcomings of prior art deactivation antennas.